洛伊盆地上三叠统沉积相与油气成藏特征

Upper Triassic Sedimentary Facies and Hydrocarbon Accumulations in Luoyang-Yichuan Basin

洛伊盆地上三叠统埋深适中、厚度大,钻井显示出较好的油气资源潜力。通过粒度分析和沉积相重建,分析洛伊盆地上三叠统沉积相及油气成藏特征。结果表明:洛伊盆地上三叠统以河流相和湖泊相为主,深湖相、浅湖相、沼泽化湖相和三角洲平原相等沉积亚相有利于油气形成;上三叠统有效烃源岩厚度约为900 m,以暗色泥岩为主;椿树腰组泥岩有机碳含量平均为0.82%;谭庄组有机碳含量平均为1.83%,有机质成熟度平均为0.69%,接近成熟生油阶段,有机质类型主要为Ⅱ_1和Ⅱ_2型。深湖相发育泥岩与砂岩互层,具有形成自生自储型油气藏的沉积条件,表现出相控油气特征;另因上三叠统顶部剥蚀,部分油气运移至古近系,可形成古生新储型油气藏;上三叠统烃源岩演化经历2个阶段,三叠纪末期进入生烃门限,但后期构造抬升使得生烃活动停止,在早古近纪末期燕山期埋深增加,再次生烃;椿树腰组与谭庄组深湖相面积约为3 700 km2,浅湖相面积约为4 100 km^2,估算生烃总量约为4.47×10~8t,具有开采潜力。洛伊盆地上三叠统为油气藏远景区,有进一步开发研究的意义。

The Upper Triassic strata with moderate buried depth and large thickness show favorable hydrocarbon resource potential by drilling. Grading test and sedimentary facies reconstruction are used to analyze the Upper Triassic sedimentary facies and hydrocarbon accumulations in Luoyang- Yichuan Basin. Research shows that the Upper Triassic sedimentary facies is dominated by fluvial and lacustrine facies,and deep lacustrine,shallow lacustrine,swampiness lacustrine,delta plain and other sedimentary subfacies are favorable to hydrocarbon generation. The thickness of Upper Triassic active source-rocks is about 900 m,which is dominated by dark mudstone. The average organic carbon content of Chunshuyao mudstone is 0. 82%.The average organic carbon content and average organic matter maturity of Tanzhuang mudstone in mature hydrocarbon-generation stage are 1. 83% and0. 69% respectively,and the organic matter is dominated by TypeⅡ1 and TypeⅡ 2. Deep lacustrine facies with well-developed mudstone-sandstone interbedding provides favorable sedimentary conditions for self-source and self-preservation hydrocarbon reservoirs,which is featured by facies-control. In addition,part of hydrocarbon migrates into the Paleogene strata due to Upper Triassic top denudation,which results in some palaeozoic new hydrocarbon reservoirs. The Upper Triassic source-rock evolution experiences two stages,the hydrocarbon generation of source-rock steps into hydrocarbon generation threshold in the late Triassic and stops due to later tectonic uplift. The hydrocarbon generation is reactivated in the late stage of early Paleogene due to the increase of buried depth. The area of deep lacustrine facies in Chunshuyao and Tanzhuang is about 3 700 km^2,the area of shallow lacustrine is about 4 100 km^2 and the estimated total hydrocarbon is about 1. 47×10~8t,which shows favorable development potential. The Upper Triassic stratum in Luoyang-Yichuan Basin is considered as a prospective hydrocarbon area,and it is of great significance to carry out further research for development.